Internet Engineering Task Force F. Brockners
Internet-Draft S. Bhandari
Intended status: Standards Track Cisco
Expires: March 5, 2012 V. Singh
V. Fajardo
Telcordia Technologies
September 2, 2011
Diameter Network Address and Port Translation Control Applicationdraft-ietf-dime-nat-control-11
Abstract
This document describes the framework, messages, and procedures for
the Diameter Network address and port translation Control
Application. This Diameter application allows per endpoint control
of Network Address Translators and Network Address and Port
Translators, which are added to networks to cope with IPv4-address
space depletion. This Diameter application allows external devices
to configure and manage a Network Address Translator device -
expanding the existing Diameter-based AAA and policy control
capabilities with a Network Address Translators and Network Address
and Port Translators control component. These external devices can
be network elements in the data plane such as a Network Access
Server, or can be more centralized control plane devices such as AAA-
servers. This Diameter application establishes a context to commonly
identify and manage endpoints on a gateway or server, and a Network
Address Translator and Network Address and Port Translator device.
This includes, for example, the control of the total number of
Network Address Translator bindings allowed or the allocation of a
specific Network Address Translator binding for a particular
endpoint. In addition, it allows Network Address Translator devices
to provide information relevant to accounting purposes.
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
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time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on March 5, 2012.
Copyright Notice
Copyright (c) 2011 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
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Internet-Draft Diameter NAT Control Application September 20111. Introduction
Internet service providers deploy Network Address Translators (NATs)
and Network Address and Port Translators (NAPTs) [RFC3022] in their
networks. A key motivation for doing so is the depletion of
available public IPv4 addresses. This document defines a Diameter
application allowing providers to control the behavior of NAT and
NAPT devices that implement IPv4-to-IPv4 network address and port
translation [RFC2663] as well as stateful IPv6-to-IPv4 address family
translation translation as defined in [RFC2663], [RFC6145], and
[RFC6146]. The use of a Diameter application allows for simple
integration into the existing Authentication, Authorization and
Accounting (AAA) environment of a provider.
The Diameter Network address and port translation Control Application
(DNCA) offers the following capabilities:
1. Limits or defines the number of NAPT/NAT bindings made available
to an individual end point or user. The main motivation for
restricting the number of bindings on a per end point basis is to
protect the service of the service provider against denial of
service attacks. If multiple end points share a single public IP
address, these end points can share fate. If one end point would
(either intentionally, or due to mis-behavior, mis-configuration,
mal-ware, etc.) be able to consume all available bindings for a
given single public IP address, service would be hampered (or
might even become unavailable) for those other end points sharing
the same public IP address. The efficiency of a NAPT deployment
depends on the maximum number of bindings an end point could use.
Given that the typical number of bindings an end point uses
depends on the type of end point (e.g. a personal computer of a
broadband user is expected to use a higher number of bindings
than a simple mobile phone) and a NAPT device is often shared by
different types of end points, it is desirable to actively manage
the maximum number of bindings. This requirement is specified in
REQ-3 of [I-D.ietf-behave-lsn-requirements]
2. Supports the allocation of specific NAPT/NAT bindings. Two types
of specific bindings can be distinguished:
* Allocation of a pre-defined NAT binding: Both the internal and
external IP address and port pair are specified within the
request. Some deployment cases, such as access to a web-
server within a user's home network with IP address and port,
benefit from statically configured bindings.
* Allocation of an external IP address for a given internal IP
address: The allocated external IP address is reported back to
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the requestor. In some deployment scenarios, the application
requires immediate knowledge of the allocated binding for a
given internal IP address but does not control the allocation
of the external IP address; for example, SIP-proxy server
deployments.
3. Defines the external address pool(s) to be used for allocating an
external IP address: External address pools can either be pre-
assigned at the NAPT/NAT device, or specified within a request.
If pre-assigned address pools are used, a request needs to
include a reference to identify the pool. Otherwise, the request
contains a description of the IP address pool(s) to be used; for
example, a list of IP-subnets. Such external address pools can
be used to select the external IP address in NAPT/NAT bindings
for multiple subscribers.
4. Generates reports and accounting records: Reports established
bindings for a particular user. The collected information is
used by accounting systems for statistical purposes.
5. Queries and retrieves details about bindings on demand: This
feature complements the previously mentioned accounting
functionality (see item 4). This feature can be used by an
entity to find NAT-bindings belonging to one or multiple end
points on the NAT-device. The entity is not required to create a
DNCA control session to perform the query, but would obviously
still need to create a Diameter session complying to the security
requirements.
6. Identifies a subscriber or endpoint on multiple network devices
(NAT/NAPT device, the AAA-server, or the Network Access Server
(NAS)): Endpoint identification is facilitated through a Global
Endpoint ID. Endpoints are identified through a single or a set
of classifiers, such as IP address, Virtual Local Area Network
(VLAN) identifier, or interface identifier which uniquely
identify the traffic associated with a particular global
endpoint.
With the above capabilities, DNCA qualifies as a MIDCOM protocol
[RFC3303], [RFC3304], [RFC5189] for middle boxes which perform NAT.
The MIDCOM protocol evaluation [RFC4097] evaluated Diameter as a
candidate protocol for MIDCOM. DNCA provides the extensions to the
Diameter base protocol [RFC3588] following the MIDCOM protocol
requirements, such as the support of NAT-specific rule transport,
support for oddity of mapped ports, as well as support for
consecutive range port numbers. DNCA adds to the MIDCOM protocol
capabilities in that it allows to maintain the reference to an end
point representing a user or subscriber in the control operation,
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enabling the control of the behavior of a NAT-device on a per end
point basis. Following the requirements of different operators and
deployments, different management protocols are employed. Examples
include e.g. SNMP [RFC3411] and NETCONF [RFC6241] which can both be
used for device configuration. Similarly, DNCA is complementing
existing MIDCOM implementations, offering a MIDCOM protocol option
for operators with an operational environment that is Diameter-
focused which desire to use Diameter to perform per end point NAT
control.
This document is structured as follows: Section 2 lists terminology,
while Section 3 provides an introduction to DNCA and its overall
deployment framework. Sections 4 to 8 cover DNCA specifics, with
Section 4 describing session management, Section 5 the use of the
Diameter base protocol, Section 6 new commands, Section 7 Attribute
Value Pairs(AVPs) used, and Section 8 accounting aspects. Section 9
presents AVP occurrence tables. IANA and security considerations are
addressed in Sections 10 and 11.
2. Conventions
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
Abbreviations used in this document:
AAA: Authentication, Authorization, Accounting
DNCA: Diameter Network address and port translation Control
Application
NAPT: Network Address and Port Translation, see also [RFC3022]
NAT: Network Address Translation (NAT and NAPT are used in this
document interchangeably)
NAT-binding or binding: Association of two IP address/port pairs
(with one IP address typically being private and the other one
public) to facilitate NAT
NAT Binding Predefined template: Is a policy template or
configuration that is predefined at the NAT-device. It may
contain NAT-bindings, IP-address pools for allocating the external
IP-address of a NAT-binding, the maximum number of allowed NAT-
bindings for end-points, etc.
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Figure 1: Typical network deployment for internet access
Figure 2 depicts the deployment scenario where a service provider
places a NAT between the host and the public Internet. The objective
is to provide the customer with connectivity to the public IPv4
Internet. The NAT-device performs network address and port (and
optionally address family) translation, depending on whether the
access network uses private IPv4 addresses or public IPv6 addresses,
to public IPv4 addresses. Note that there may be more than one NAS,
NAT-device, or AAA-entity in a deployment, although the figures only
depict one entity each for clarity.
If the NAT-device would be put in place without any endpoint
awareness, the service offerings of the service provider could be
impacted as detailed in [I-D.ietf-behave-lsn-requirements]. This
includes cases like:
o Provisioning static NAT bindings for particular endpoints
o Using different public IP address pools for different set of
endpoints (for example, residential or business customers)
o Reporting allocated bindings on a per endpoint basis
o Integrate control of the NAT-device into the already existing per
endpoint management infrastructure of the service provider
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+---------+
| |
| AAA |
| |
+---------+
|
|
|
|
+--------+ +---------+ +--------+ +----------+
| | | | | | | |
| Host |----| NAS |----| NAT- |----| IPv4- |
| | | | | device | | Internet |
+--------+ +---------+ +--------+ +----------+
For NAT44 deployments (IPv4 host):
<----- Private IPv4 ----------><--- Public IPv4 --->
For NAT64 deployments (IPv6 host):
<----- Public IPv6 ----------><--- Public IPv4 --->
Figure 2: Access network deployment with NAT
Figure 2 shows a typical deployment for IPv4-Internet access
involving a NAT-device within the service provider network. The
figure describes two scenarios: One where an IPv4-host (with a
private IPv4 address) accesses the IPv4-Internet, as well as one
where an IPv6-host accesses the IPv4-Internet.
3.2. Diameter NAPT Control Application Overview
DNCA runs between two DNCA Diameter peers. One DNCA Diameter peer
resides within the NAT-device, the other DNCA Diameter peer resides
within a NAT-controller (discussed in Section 3.3). DNCA allows per
endpoint control and management of NAT within the NAT-device. Based
on Diameter, DNCA integrates well with the suite of Diameter
applications deployed for per endpoint authentication, authorization,
accounting, and policy control in service provider networks.
DNCA offers:
o Request and answer commands to control the allowed number of NAT
bindings per endpoint to request the allocation of specific
bindings for an endpoint, to define the address pool to be used
for an endpoint.
o Provides per endpoint reporting of the allocated NAT bindings.
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o Provides unique identification of an endpoint on NAT-device, AAA-
server and NAS, to simplify correlation of accounting data
streams.
DNCA allows controlling the behavior of a NAT-device on a per
endpoint basis during initial session establishment and at later
stages by providing an update procedure for already established
sessions. Using DNCA, per endpoint NAT binding information can be
retrieved either using accounting mechanisms or through an explicit
session query to the NAT.
3.3. Deployment Scenarios For DNCA
DNCA can be deployed in different ways. DNCA supports deployments
with "n" NAT-controllers and "m" NAT-devices, with n and m equal to
or greater than 1. For DNCA, the session representing a particular
endpoint is atomic. Any deployment MUST ensure that for every given
endpoint only a single NAT-controller and only a single NAT-device
are active at any point in time. This is to ensure that NAT-devices
controlled by multiple NAT-controllers do not receive conflicting
control requests for a particular endpoint, or would be unclear which
NAT-controller to send accounting information to.
Two common deployment scenarios are outlined in Figure 3 ("integrated
deployment") and Figure 4 ("autonomous deployment"). Per the note
above, multiple instances of NAT-controllers and NAT-devices could be
deployed. The figures only show single instances for reasons of
clarity. The two shown scenarios differ in which entity fulfills the
role of the NAT-controller. Within the figures (C) denotes the
network element performing the role of the NAT-controller.
The integrated deployment approach hides the existence of the NAT-
device from external servers, such as the AAA-server. It is suited
for environments where minimal changes to the existing AAA deployment
are desired. The NAS and the NAT-device are Diameter peers
supporting the DNCA. The Diameter peer within the NAS, performing
the role of the NAT-controller, initiates and manages sessions with
the NAT-device, exchanges NAT specific configuration information and
handles reporting and accounting information. The NAS receives
reporting and accounting information from the NAT-device. With this
information, the NAS can provide a single accounting record for the
endpoint. A system correlating the accounting information received
from the NAS and NAT-device would not be needed.
An example network attachment for an integrated NAT deployment can be
described as follows: An endpoint connects to the network, with the
NAS being the point of attachment. After successful authentication,
the NAS receives endpoint related authorization data from the AAA-
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server. A portion of the authorization data applies to per endpoint
configuration on the NAS itself, another portion describes
authorization and configuration information for NAT control aimed at
the NAT-device. The NAS initiates a DNCA session to the NAT-device
and sends relevant authorization and configuration information for
the particular endpoint to the NAT-device. This can comprise NAT-
bindings, which have to be pre-established for the endpoint, or
management related configuration, such as the maximum number of NAT-
bindings allowed for the endpoint. The NAT-device sends its per
endpoint accounting information to the NAS, which aggregates the
accounting information received from the NAT-device with its local
accounting information for the endpoint into a single accounting
stream towards the AAA-server.
+---------+
| |
| AAA |
| |
+---------+
|
|
|
+--------+ +---------+ +--------+ +----------+
| | | (C) | | | | |
| Host |----| NAS |----| NAT- |----| IPv4- |
| | | | | device | | Internet |
+--------+ +---------+ +--------+ +----------+
For NAT44 deployments (IPv4 host):
<----- Private IPv4 ----------><--- Public IPv4 --->
For NAT64 deployments (IPv6 host):
<----- Public IPv6 ----------><--- Public IPv4 --->
Figure 3: NAT control deployment: Integrated deployment
Figure 3 shows examples of integrated deployments. The figure
describes two scenarios: One where an IPv4-host (with a private IPv4
address) accesses the IPv4-Internet, as well as one where an IPv6-
host accesses the IPv4-Internet.
The autonomous deployment approach decouples user management on the
NAS and NAT-device. In the autonomous deployment approach, the AAA-
system and the NAT-device are the Diameter peers running the DNCA.
The AAA-system also serves as NAT-controller. It manages the
connection to the NAT-device, controls the per endpoint
configuration, and also receives accounting and reporting information
from the NAT-device. Different from the integrated deployment
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scenario, the autonomous deployment scenario does not "hide" the
existence of the NAT-device from the AAA infrastructure. Here two
accounting streams are received by the AAA-server for one particular
endpoint, one from the NAS, and one from the NAT-device.
+---------+
| (C) |
| AAA |---------
| | |
+---------+ |
| |
| |
| |
+--------+ +---------+ +---------+ +----------+
| IPv4/ | | | | | | IPv4 |
| IPv6 |----| NAS |----| NAT- |----| Internet |
| Host | | | | device | | |
+--------+ +---------+ +---------+ +----------+
For NAT44 deployments (IPv4 host):
<----- Private IPv4 ----------><--- Public IPv4 --->
For NAT64 deployments (IPv6 host):
<----- Public IPv6 ----------><--- Public IPv4 --->
Figure 4: NAT control deployment: Autonomous deployment
Figure 4 shows examples of autonomous deployments. The figure
describes two scenarios: One where an IPv4-host (with a private IPv4
address) accesses the IPv4-Internet, as well as one where an IPv6-
host accesses the IPv4-Internet.
4. DNCA Session Establishment and Management
Note that this section forward references some of the commands and
AVPs defined for DNCA. Please refer to Section 6 and Section 8 for
details. DNCA runs between a Diameter peer residing in a NAT-
controller and a Diameter peer residing in a NAT-device. The
Diameter peer within the NAT-controller is always the control
requesting entity: It initiates, updates, or terminates the sessions.
Sessions are initiated when the NAT-controller learns about a new
endpoint (i.e., host) that requires a NAT service. This could for
example be due to the entity hosting the NAT-controller receiving
authentication, authorization, or accounting requests for or from the
endpoint. Alternate methods that could trigger session setup include
local configuration, receipt of a packet from a formerly unknown IP-
address, etc.
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Internet-Draft Diameter NAT Control Application September 20114.1. Session Establishment
The DNCA Diameter peer within the NAT-controller establishes a
session with the DNCA Diameter peer within the NAT-device to control
the behavior of the NAT function within the NAT-device. During
session establishment, the DNCA Diameter peer within the NAT-
controller passes along configuration information to DNCA Diameter
peer within the NAT-device. The session configuration information
comprises the maximum number of bindings allowed for the endpoint
associated with this session, a set of pre-defined NAT bindings to be
established for this endpoint, or a description of the address pool,
that external addresses are to be allocated from.
The DNCA Diameter peer within the NAT-controller generates a NAT-
Control Request (NCR) message to the DNCA Diameter peer within the
NAT-device with NC-Request-Type AVP set to INITIAL_REQUEST to
initiate a Diameter NAT control session. On receipt of a NCR the
DNCA Diameter peer within the NAT-device sets up a new session for
the endpoint associated with the endpoint classifier(s) contained in
the NCR. The DNCA Diameter peer within the NAT-device notifies its
DNCA Diameter peer within the NAT-controller about successful session
setup using a NAT-Control Answer (NCA) message with Result-Code set
to DIAMETER_SUCCESS. Figure 5 shows the initial protocol interaction
between the two DNCA Diameter peers.
The initial NAT-Control-Request MAY contain configuration information
for the session, which specifies the behavior of the NAT-device for
the session. The configuration information that MAY be included,
comprises:
o A list of NAT bindings, which should be pre-allocated for the
session; for example, in case a user requires a fixed external IP-
address/port pair for one of his applications.
o The maximum number of NAT-bindings allowed for an endpoint.
o A description of the external IP-address pool(s) to be used for
the session.
o A reference to a NAT Binding Predefined template on the NAT-
device, which is applied to the session. Such a NAT Binding
Predefined template on the NAT-device may contain, for example,
the name of the IP-address pool that external IP-addresses should
be allocated from, the maximum number of bindings permitted for
the endpoint, etc.
In certain cases, the NAT-device may not be able to perform the tasks
requested within the NCR. These include the following:
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o If a DNCA Diameter peer within the NAT-device receives a NCR from
a DNCA Diameter peer within a NAT-controller with NC-Request-Type
AVP set to INITIAL_REQUEST that identifies an already existing
session; that is, DNCA Diameter peer and endpoint identifier match
an already existing session, the DNCA Diameter peer within the
NAT-device MUST return an NCA with Result-Code set to
SESSION_EXISTS, and provide the Session-Id of the existing session
in the Duplicate-Session-Id AVP.
o If a DNCA Diameter peer within the NAT-device receives a NCR from
a DNCA Diameter peer within a NAT-controller with NC-Request-Type
AVP set to INITIAL_REQUEST that matches more than one of the
already existing sessions; that is, DNCA Diameter peer and
endpoint identifier match already existing sessions, the DNCA
Diameter peer within the NAT-device MUST return an NCA with
Result-Code set to INSUFFICIENT-CLASSIFIERS. In case a DNCA
Diameter peer receives a NCA that reports Insufficient-
Classifiers, it MAY choose to retry establishing a new session
using additional or more specific classifiers.
o If the NCR contains a NAT Binding Predefined template not defined
on the NAT-device, the DNCA Diameter peer within the NAT-device
MUST return an NCA with Result-Code AVP set to
UNKNOWN_BINDING_TEMPLATE_NAME.
o In case the NAT-device is unable to establish all of the bindings
requested in the NCR, the DNCA Diameter peer MUST return an NCA
with Result-Code set to BINDING_FAILURE. A DNCA Diameter peer
within a NAT-device MUST treat a NCR as an atomic operation; hence
none of the requested bindings will be established by the NAT-
device. Either all requested actions within a NCR MUST be
completed successfully, or the entire request fails.
o If a NAT-device does not have sufficient resources to process a
request, the DNCA Diameter peer MUST return an NCA with Result-
Code set to RESOURCE_FAILURE.
o In case Max-NAT-Binding, NAT-Control-Definition as well as NAT-
Control-Binding-Template are included in the NCR, and the values
in Max-NAT-Binding and NAT-Control-Definition contradict those
specified in the pre-provisioned template on the NAT-device which
NAT-Control-Binding-Template references, Max-NAT-Binding and NAT-
Control-Definition MUST override the values specified in the
template that NAT-Control-Binding-Template refers to.
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NAT-controller (DNCA Diameter peer) NAT-device (DNCA Diameter peer)
| |
| |
| |
Trigger |
| |
| NCR |
|------------------------------------------>|
| |
| |
| |
| |
| If Able to comply
| with Request then
| Create session state
| |
| |
| NCA |
|<------------------------------------------|
| |
| |
Figure 5: Initial NAT control request and session establishment
Note: The DNCA Diameter peer within the NAT-device creates session
state only if it is able to comply with the NCR. On success it will
reply with an NCA with Result-Code set to DIAMETER_SUCCESS.
4.2. Session Re-Authorization
Session re-authorization is performed if the NAT-controller desires
to change the behavior of the NAT-device for an existing session.
Session re-authorization could be used, for example, to change the
number of allowed bindings for a particular session, or establish or
remove a pre-defined binding.
The DNCA Diameter peer within the NAT-controller generates a NCR
message to the DNCA Diameter peer within the NAT-device with NC-
Request-Type AVP set to UPDATE_REQUEST upon receiving a trigger
signal. If the session is updated successfully, the DNCA Diameter
peer within the NAT-device notifies the DNCA Diameter peer within the
NAT-controller about the successful session update using a NAT-
Control Answer (NCA) message with Result-Code set to
DIAMETER_SUCCESS. Figure 6 shows the protocol interaction between
the two DNCA Diameter peers.
In certain cases, the NAT-device may not be able to perform the tasks
requested within the NCR. These include the following:
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o If DNCA Diameter peer within a NAT-device receives an NCR update
or query request for a non-existent session, it MUST set Result-
Code in the answer to DIAMETER_UNKNOWN_SESSION_ID.
o If the NCR contains a NAT Binding Predefined template not defined
on the NAT-device, an NCA with Result-Code AVP set to
UNKNOWN_BINDING_TEMPLATE_NAME MUST be returned.
o If the NAT-device cannot establish the requested binding because
the maximum number of allowed bindings has been reached for the
endpoint classifier, an NCA with Result-Code AVP set to
MAXIMUM_BINDINGS_REACHED_FOR_ENDPOINT MUST be returned to the DNCA
Diameter peer.
o If the NAT-device cannot establish some or all of the bindings
requested in an NCR, but has not yet reached the maximum number of
allowed bindings for the endpoint, an NCA with Result-Code set to
BINDING_FAILURE MUST be returned. As already noted, the DNCA
Diameter peer in a NAT-device MUST treat an NCR as an atomic
operation. Hence none of the requested bindings will be
established by the NAT-device in case of failure. Actions
requested within a NCR are either all successful or all fail.
o If the NAT-device does not have sufficient resources to process a
request, an NCA with Result-Code set to RESOURCE_FAILURE MUST be
returned.
o If an NCR redefines the maximum number of NAT-bindings allowed for
the endpoint, the new value MUST override any previously defined
limit on NAT bindings. It depends on the implementation of the
NAT-device on how the NAT-device copes with a case where the new
value is lower than the actual number of allocated bindings. The
NAT-device SHOULD refrain from enforcing the new limit immediately
(that is, actively remove bindings), but rather disallows the
establishment of new bindings until the current number of bindings
is lower than the newly established maximum number of allowed
bindings.
o If an NCR specifies a new NAT Binding Predefined template on the
NAT-device, the NAT Binding Predefined template overrides any
previously defined rule for the session. Existing NAT-bindings
SHOULD NOT be impacted by the change of templates.
o In case Max-NAT-Binding, NAT-Control-Definition as well as NAT-
Control-Binding-Template are included in the NCR, and the values
in Max-NAT-Binding and NAT-Control-Definition contradict those
specified in the pre-provisioned template on the NAT-device which
NAT-Control-Binding-Template references, Max-NAT-Binding and NAT-
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Control-Definition MUST override the values specified in the
template that the NAT-Control-Binding-Template refers to.
Note: Already established bindings for the session SHOULD NOT be
affected in case the tasks requested within the NCR cannot be
completed.
NAT-controller (DNCA Diameter peer) NAT-device (DNCA Diameter peer)
| |
| |
| |
Change of session |
attributes |
| |
| NCR |
|------------------------------------------>|
| |
| |
| If able to comply
| with the request:
| Update session state
| |
| |
| NCA |
|<------------------------------------------|
| |
Figure 6: NAT control request for session update
4.3. Session and Binding Query
A Session and NAT-binding query MAY be used by the DNCA Diameter peer
within the NAT-controller to either retrieve information on the
current bindings for a particular session at the NAT-device or
discover the session identifier for a particular external IP address/
port pair.
A DNCA Diameter peer within the NAT-controller starts a session query
by sending an NCR message with NC-Request-Type AVP set to
QUERY_REQUEST. Figure 7 shows the protocol interaction between the
DNCA Diameter peers.
Two types of query requests exist. The first type of query request
uses the session ID as input parameter to the query. It is to allow
the DNCA Diameter peer within the NAT-controller to retrieve the
current set of bindings for a specific session. The second type of
query request is used to retrieve the session identifiers, along with
the associated bindings, matching a criteria. This enables the DNCA
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Diameter peer within the NAT-controller to find those sessions, which
utilize a specific external IP-address.
1. Request a list of currently allocated NAT bindings for a
particular session: On receiving a NCR, the NAT-device SHOULD
look up the session information for the session ID contained in
the NCR, and report all currently active NAT-bindings for the
session using an NCA message with Result-Code set to
DIAMETER_SUCCESS. In this case the NCR MUST NOT contain a NAT-
Control-Definition AVP. Each NAT-binding is reported in a NAT-
Control-Definition AVP. In case the session ID is unknown, the
DNCA Diameter peer within the NAT-device MUST return an NCA
message with Result-Code set to DIAMETER_UNKNOWN_SESSION_ID.
2. Retrieve session IDs and internal IP address/port pairs for one
or multiple external IP-address/port pairs: If the DNCA Diameter
peer within the NAT-controller wishes to retrieve the session
ID(s) for one or multiple external IP-address/port pairs, it MUST
include the external IP-address/port pair(s) as part of the NAT-
Control-Definition AVP of the NCR. The external IP-address/port
pair(s) are pre-known to the controller via configuration, AAA
interactions, or other means. The session ID is not included in
the NCR or the NCA for this type of a query. The DNCA Diameter
peer within the NAT-device SHOULD report the NAT-bindings and
associated session IDs corresponding to the external IP-address/
port pairs in an NCA message using one or multiple instances of
the NAT-Control-Definition AVP. The Result-Code is set to
DIAMETER_SUCCESS. In case an external IP-address/port pair has
no associated existing NAT-binding, the NAT-Control-Definition
AVP contained in the reply just contains the NAT-External-Address
AVP.
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NAT-controller (DNCA Diameter peer) NAT-device (DNCA Diameter peer)
| |
| |
| |
DNCA Session Established |
| |
| NCR |
|------------------------------------------>|
| |
| |
| |
| |
| Look up corresponding session
| and associated NAT-bindings
| |
| NCA |
|<------------------------------------------|
| |
| |
| |
Figure 7: Session query
4.4. Session Termination
Similar to session initiation, session tear down MUST be initiated by
the DNCA Diameter peer within the NAT-controller. The DNCA Diameter
peer sends a Session Terminate Request (STR) message to its peer
within the NAT-device upon receiving a trigger signal. The source of
the trigger signal is outside the scope of this document. As part of
STR message processing the DNCA Diameter peer within the NAT-device
MAY send an accounting stop record reporting all bindings. All the
NAT-bindings belonging to the session MUST be removed and the session
state MUST be cleaned up. The DNCA Diameter peer within the NAT-
device MUST notify its DNCA Diameter peer in the NAT-controller about
successful session termination using a Session Terminate Answer (STA)
message with Result-Code set to DIAMETER_SUCCESS. Figure 8 shows the
protocol interaction between the two DNCA Diameter peers.
If a DNCA Diameter peer within a NAT-device receives a STR and fails
to find a matching session, the DNCA Diameter peer MUST return a STA
with Result-Code set to DIAMETER_UNKNOWN_SESSION_ID.
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within the NAT-controller is unable to comply with the ASR for any
other reason, an ASA with Result-Code set to
DIAMETER_UNABLE_TO_COMPLY MUST be returned.
NAT-controller (DNCA Diameter peer) NAT-device (DNCA Diameter peer)
| |
| |
| Trigger
| |
| ASR |
|<-------------------------------------------|
| |
| |
| |
| ASA |
|------------------------------------------->|
| |
| |
| |
| On successful ASA |
|<------Session Termination Procedure------->|
Figure 9: Abort NAT control session
4.6. Failure cases of the DNCA Diameter peers
This document does not specify the behavior in case the NAT-device
and NAT-controller, or their respective DNCA Diameter peers are out
of sync or lose state. This could happen for example if one of the
entities restarts, in case of a (temporary) loss of network
connectivity etc. Example failure cases include the following:
o NAT-controller and the DNCA Diameter peer within the NAT-
controller lose state (e.g., due to a restart). In this case,
* the DNCA Diameter peer within the NAT-device MAY receive an NCR
with NC-Request-Type AVP set to INITIAL_REQUEST that matches an
existing session of the DNCA Diameter peer within the NAT-
device. The DNCA Diameter peer within the NAT-device MUST
return Result-Code that contains Duplicate-Session-Id AVP to
report the Session-ID of the existing session. The DNCA
Diameter peer within the NAT-controller MAY send an explicit
Session Terminate Request (STR) for the older session, which
was lost.
* a DNCA Diameter peer MAY receive accounting records for a
session that does not exist. The DNCA Diameter peer sends an
accounting answer with Result-Code set to
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DIAMETER_UNKNOWN_SESSION_ID in response. On receiving the
response, the DNCA Diameter peer SHOULD clear the session and
remove associated session state.
o NAT-device and the DNCA Diameter peer within NAT-device lose
state. In such a case, the DNCA Diameter peer MAY receive a NCR
with NC-Request-Type AVP set to UPDATE_REQUEST for a non-existent
session. The DNCA Diameter peer MUST return an NCA with Result-
Code set to DIAMETER_UNKNOWN_SESSION_ID.
o The DNCA Diameter peer within the NAT-controller is unreachable,
for example detected by Diameter device watchdog messages (as
defined in Section 5.5 of [RFC3588]), or down and accounting
requests from the DNCA Diameter peer fail to get a response. The
mechanism to ensure that a DNCA Diameter peer within the NAT-
controller no longer has associated state for a session which was
cleared or removed by the DNCA Diameter peer within the NAT-device
is beyond the scope of this document.
o The DNCA Diameter peer within the NAT-device is unreachable or
down and NCR fails to get a response. Handling of this case
depends on the actual service offering of the service provider.
The service provider could for example choose to stop offering
connectivity service.
5. Use of the Diameter Base Protocol
The Diameter Base Protocol defined by [RFC3588] applies with the
clarifications listed in the present specification.
5.1. Securing Diameter Messages
For secure transport of Diameter messages, the recommendations in
[RFC3588] apply.
DNCA Diameter peers SHOULD verify their identity during the
Capabilities Exchange Request procedure.
A DNCA Diameter peer within the NAT-device SHOULD verify that a DNCA
Diameter peer that issues a NCR command is allowed to do so based on:
o The identity of the DNCA Diameter peer
o The type of NCR Command
o The content of the NCR Command
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o Any combination of the above
5.2. Accounting Functionality
Accounting functionality (accounting session state machine, related
command codes and AVPs) is defined in Section 9 below.
5.3. Use of Sessions
Each DNCA session MUST have a globally unique Session-ID as defined
in [RFC3588], which MUST NOT be changed during the lifetime of a DNCA
session. The Diameter Session-ID serves as the global endpoint
identifier. The DNCA Diameter peers maintain state associated with
the Session-ID. This globally unique Session-ID is used for
updating, accounting, and terminating the session. A DNCA session
MUST NOT have more than one outstanding request at any given instant.
A DNCA Diameter peer sends an Abort-Session-Request as defined in
[RFC3588] if it is unable to maintain sessions due to resource
limitation.
5.4. Routing Considerations
It is assumed that the DNCA Diameter peer within a NAT-controller
knows the DiameterIdentity of the Diameter peer within a NAT-device
for a given endpoint. Both the Destination-Realm and Destination-
Host AVPs are present in the request from a DNCA Diameter peer within
a NAT-controller to a DNCA Diameter peer within a NAT-device.
5.5. Advertising Application Support
Diameter nodes conforming to this specification MUST advertise
support for DNCA by including the value of TBD in the Auth-
Application-Id of the Capabilities-Exchange-Request and Capabilities-
Exchange-Answer command[RFC3588].
6. DNCA Commands
The following commands are used to establish, maintain and query NAT-
bindings.
6.1. NAT-Control Request (NCR) Command
The NAT-Control Request (NCR) command, indicated by the command field
set to TBD and the "R" bit set in the Command Flags field, is sent
from the DNCA Diameter peer within the NAT-controller to the DNCA
Diameter peer within the NAT-device in order to install NAT-bindings.
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<NC-Answer> ::= < Diameter Header: TBD, PXY >
[ Session-Id ]
{ Origin-Host }
{ Origin-Realm }
{ Result-Code }
[ NC-Request-Type ]
* [ NAT-Control-Definition ]
[ Current-NAT-Bindings ]
[ Origin-State-Id ]
[ Error-Message ]
[ Error-Reporting-Host ]
* [ Failed-AVP ]
* [ Proxy-Info ]
[ Duplicate-Session-ID ]
* [ Redirect-Host]
[ Redirect-Host-Usage ]
[ Redirect-Max-Cache-Time ]
* [ Proxy-Info ]
* [ Route-Record ]
* [ Failed-AVP ]
* [ AVP ]
7. NAT Control Application Session State Machine
This section contains a set of finite state machines, representing
the life cycle of a DNCA session, which MUST be observed by all
implementations of the DNCA Diameter application. The DNCA Diameter
peers are stateful and the state machine maintained is similar to the
stateful Client and Server authorization state machine described in
[RFC3588]. When a session is moved to the Idle state, any resources
that were allocated for the particular session must be released. Any
event not listed in the state machines MUST be considered as an error
condition, and an answer, if applicable, MUST be returned to the
originator of the message.
In the state table, the event 'Failure to send NCR' means that the
DNCA Diameter peer within the NAT-controller is unable to send the
NCR command to the desired destination. This could be due to the
peer being down, or due to the peer sending back the transient
failure or temporary protocol error notification DIAMETER_TOO_BUSY or
DIAMETER_LOOP_DETECTED in the Result-Code AVP of an NCA.
In the state table "FAILED NCA" means that the DNCA Diameter peer
within the NAT-device was not able to honor the corresponding NCR.
This can happen due to any transient and permanent error at the NAT-
device or its associated DNCA Diameter peer within indicated by the
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following error Result-Code values: RESOURCE_FAILURE,
UNKNOWN_BINDING_TEMPLATE_NAME, BINDING_FAILURE,
MAXIMUM_BINDINGS_REACHED_FOR_ENDPOINT, SESSION_EXISTS,
INSUFFICIENT_CLASSIFIERS.
The following state machine is observed by a DNCA Diameter peer
within a NAT-controller. The state machine description uses the term
"access session" to describe the connectivity service offered to the
endpoint or host. "Access session" should not be confused with the
Diameter session ID.
DNCA Diameter peer within a NAT-controller
State Event Action New State
-------------------------------------------------------------
Idle New endpoint detected that Send Pending
requires NAT Control NCR
Initial
Request
Idle ASR Received Send ASA Idle
for unknown session with
Result-Code
= UNKNOWN_
SESSION_ID
Pending Successful NCA Setup Open
received complete
Pending Successful NCA Send STR Discon
received
but peer unable to provide
service
Pending Error processing successful Send STR Discon
NCA
Pending Failed Clean up Idle
NCA received
Open NAT control Send Open
update required NCR Update
Request
Open Successful Open
NCA received
Open Failed Clean up Idle
NCA received
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Open Access session end detected Send STR Discon
Open ASR Received, Send ASA Discon
access session will be with
terminated Result-Code
= SUCCESS,
Send STR
Open ASR Received, Send ASA Open
access session will not with
be terminated Result-Code
!= SUCCESS
Discon ASR Received Send ASA Idle
Discon STA Received Discon. Idle
user/device
The following state machine is observed by a DNCA Diameter peer
within a NAT-device.
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DNCA Diameter peer within a NAT-device
State Event Action New State
-------------------------------------------------------------
Idle NCR Query request Send Idle
received, and successful
able to provide requested NCA
NAT Binding report
Idle NCR received Send Open
and able to successful
provide requested NCA
NAT control service
Idle NCR request Send Idle
received, and failed
unable to provide requested NCA
NAT control service
Open NCR request Send Open
received, and successful
able to provide requested NCA
NAT control service
Open NCR request Send Idle
received, and failed
unable to provide requested NCA,
NAT control service Clean up
Open Unable to continue Send ASR Discon
providing requested
NAT control service
Discon Failure to send ASR Wait, Discon
resend ASR
Discon ASR successfully sent and Clean up Idle
ASA Received with Result-Code
Not ASA Received None No change
Discon
Any STR Received Send STA, Idle
Clean up
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Internet-Draft Diameter NAT Control Application September 20118.2.2. Transient Failures
Result-Code AVP values that fall within the transient failures
category are those used to inform a peer that the request could not
be satisfied at the time that it was received. The request may be
able to be satisfied in the future.
The following new values of the Result-Code AVP are defined:
RESOURCE_FAILURE (TBD)
The DNCA Diameter peer within the NAT-device indicates that the
binding could not be installed or a new session could not be
created due to resource shortage.
8.2.3. Permanent Failures
The Result-Code AVP values, which fall within the permanent failures
category are used to inform the peer that the request failed, and
should not be attempted again. The request may be able to be
satisfied in the future.
The following new values of the Result-Code AVP are defined:
UNKNOWN_BINDING_TEMPLATE_NAME (TBD)
The DNCA Diameter peer within the NAT-device indicates that the
binding could not be installed or a new session could not be
created because the specified NAT-Control-Binding-Template AVP,
that refers to a predefined policy template in the NAT-device,
is unknown.
BINDING_FAILURE (TBD)
DNCA indicates that the requested binding(s) could not be
installed. For example: Requested ports are already in use.
MAXIMUM_BINDINGS_REACHED_FOR_ENDPOINT (TBD)
The DNCA Diameter peer within the NAT-device denies the request
because the maximum number of allowed bindings has been reached
for the specified endpoint classifier.
SESSION_EXISTS (TBD)
The DNCA Diameter peer within the NAT-device denies request to
initialize a new session, if it already has a DNCA session that
uses the same set of classifiers as indicated by the DNCA
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QUERY_REQUEST (3)
Query Request is used to query a NAT-device about the currently
installed bindings for an endpoint classifier.
8.7.2. NAT-Control-Install AVP
The NAT-Control AVP (AVP code TBD) is of type Grouped, and it is used
to activate or install NAT bindings. It also contains Max-NAT-
Bindings that defines the maximum number of NAT bindings allowed for
an end point and the NAT-Control-Binding-Template that references a
predefined template on the NAT-device that may contain static
binding, a maximum number of bindings allowed, an IP-address pool
from which external binding addresses should be allocated, etc. If
the NAT-External-Port-Style AVP is present, then the NAT-device MUST
select the external ports for the NAT-Bindings as per the style
specified. The NAT-External-Port-Style is applicable for NAT-
Bindings defined by the NAT-Control-Definition AVPs whose NAT-
External-Address or Port AVPs within the NAT-External-Address are
unspecified.
AVP format:
NAT-Control-Install ::= < AVP Header: TBD >
* [ NAT-Control-Definition ]
[ NAT-Control-Binding-Template ]
[ Max-NAT-Bindings ]
[ NAT-External-Port-Style ]
* [ AVP ]
8.7.3. NAT-Control-Remove AVP
The NAT-Control-Remove AVP (AVP code TBD) is of type Grouped, and it
is used to deactivate or remove NAT-bindings. At least one of the
two AVPs (NAT-Control-Definition AVP, NAT-Control-Binding-Template
AVP) SHOULD be present in the NAT-Control-Remove AVP.
AVP format:
NAT-Control-Remove ::= < AVP Header: TBD >
* [ NAT-Control-Definition ]
[ NAT-Control-Binding-Template ]
* [ AVP ]
8.7.4. NAT-Control-Definition AVP
The NAT-Control-Definition AVP (AVP code TBD) is of type Grouped, and
it describes a binding.
The NAT-Control-Definition AVP uniquely identifies the binding
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between the DNCA Diameter peers.
If both the NAT-Internal-Address and NAT-External-Address AVP(s) are
supplied, it is a pre-defined binding.
If the NAT-External-Address AVP is not specified then the NAT-device
MUST select the external port as per the NAT-External-Port-Style AVP,
if present in the NAT-Control-Definition AVP.
The Protocol AVP describes the transport protocol for the binding.
The NAT-Control-Definition AVP can contain either zero or one
Protocol AVP. If the Protocol AVP is omitted and if both internal
and external IP-address are specified then the binding reserves the
IP-addresses for all transport protocols.
The Direction AVP is of type Enumerated. It specifies the direction
for the binding. The values of the enumeration applicable in this
context are: "IN","OUT". If Direction AVP is OUT or absent, the NAT-
Internal-Address refers to the IP-address of the endpoint that needs
to be translated. If Direction AVP is "IN", NAT-Internal-Address is
the destination IP-address that has to be translated.
AVP format:
NAT-Control-Definition ::= < AVP Header: TBD >
{ NAT-Internal-Address }
[ Protocol ]
[ Direction ]
[ NAT-External-Address ]
[ Session-Id ]
* [ AVP ]
8.7.5. NAT-Internal-Address AVP
The NAT-Internal-Address AVP (AVP code TBD) is of type Grouped. It
describes the internal IP-address and port for a binding. Framed-
IPV6-Prefix and Framed-IP-Address AVPs are mutually exclusive.
AVP format:
NAT-Internal-Address ::= < AVP Header: TBD >
[ Framed-IP-Address ]
[ Framed-IPv6-Prefix ]
[ Port]
* [ AVP ]
8.7.6. NAT-External-Address AVP
The NAT-External-Address AVP (AVP code TBD) is of type Grouped, and
it describes the external IP-address and port for a binding. The
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external IP-address specified in this attribute can be reused for
multiple endpoints by specifying the same address in the respective
NAT-External-Address AVPs. If the external IP-address is not
specified and the NAT-External-Port-Style AVP is specified in the
NAT-Control-Definition AVP then the NAT-device MUST select external
port as per the NAT-External-Port-Style AVP.
AVP format:
NAT-External-Address ::= < AVP Header: TBD >
[ Framed-IP-Address ]
[ Port ]
* [ AVP ]
8.7.7. Max-NAT-Bindings
The Max-NAT-Bindings AVP (AVP code TBD) is of type Unsigned32. It
indicates the maximum number of NAT-bindings allowed for a particular
endpoint.
8.7.8. NAT-Control-Binding-Template AVP
The NAT-Control-Binding-Template AVP (AVP code TBD) is of type
OctetString. It defines a name for a policy template that is
predefined at the NAT-device. Details on the contents and structure
of the template and configuration are outside the scope of this
document. The policy to which this AVP refers to may contain NAT-
bindings, IP-address pool for allocating the external IP-address of a
NAT-binding, and maximum number of allowed NAT-bindings. Such policy
template can be reused by specifying the same NAT-Control-Binding-
Template AVP in the corresponding NAT-Control-Install AVPs of
multiple endpoints.
8.7.9. Duplicate-Session-Id AVP
The Duplicate-Session-Id AVP (AVP Code TBD) is of type UTF8String.
It is used to report errors and contains the Session-Id of an
existing session.
8.7.10. NAT-External-Port-Style AVP
The NAT-External-Port-Style AVP (AVP Code TBD) is of type Enumerated
and contains the style to be followed while selecting the external
port for a NAT-Binding relative to the internal port.
The following values are defined:
FOLLOW_INTERNAL_PORT_STYLE (1)
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External port numbers selected MUST follow the same sequence
and oddity as the internal ports of the NAT-bindings. The port
odditity is required to support protocols like RTP and RTCP as
defined in [RFC3550]. If for example the internal port in a
requested NAT-binding is odd numbered then the external port
allocated MUST also be odd numbered, and vice versa for an even
numbered port. In addition, the sequence of port numbering is
maintained: If internal ports are consecutive, then the NAT-
device MUST choose consecutive external ports for the NAT-
bindings.
9. Accounting Commands
The DNCA reuses session based accounting as defined in the Diameter
Base Protocol[RFC3588] to report the bindings per endpoint. This
reporting is achieved by sending Diameter Accounting Requests (ACR)
[Start, Interim and Stop] from the DNCA Diameter peer within the NAT-
device to its associated DNCA Diameter peer within the NAT-
controller.
The DNCA Diameter peer within the NAT-device sends an ACR Start on
receiving a NCR with NC-Request-Type AVP set to INITIAL_REQUEST for a
session or on creation of the first binding for a session requested
in an earlier NCR. DNCA may send ACR Interim updates, if required,
either due to a change in bindings resulting from a NCR with NC-
Request-Type AVP set to UPDATE_REQUEST, or periodically as specified
in Acct-Interim-Interval by the DNCA Diameter peer within the NAT-
controller, or when it creates or tears down bindings. An ACR Stop
is sent by the DNCA Diameter peer within the NAT-device on receiving
STR.
The function of correlating the multiple bindings used by an endpoint
at any given time is relegated to the post processor.
The DNCA Diameter peer within the NAT-device may trigger an interim
accounting record when the maximum number of bindings, if received in
an NCR, is reached.
9.1. NAT Control Accounting Messages
The ACR and ACA messages are reused as defined in the Diameter Base
Protocol [RFC3588] for exchanging endpoint NAT binding details
between the DNCA Diameter peers. The DNCA Application IDs is used in
the accounting commands. ACR contains one or more optional NAT-
Control-Record AVPs to report the bindings. The NAT-device indicates
the number of allocated NAT bindings to the NAT-controller using the
Current-NAT-Bindings AVP. This number needs to match the number of
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bindings identified as active within the NAT-Control-Record AVP.
9.2. NAT Control Accounting AVPs
In addition to AVPs for ACR specified in [RFC3588], the DNCA Diameter
peer within the NAT-device must add the NAT-Control-Record AVP.
9.2.1. NAT-Control-Record
The NAT-Control-Record AVP (AVP code TBD) is of type Grouped. It
describes a binding and its status. If NAT-Control-Binding-Status is
set to Created, Event-Timestamp indicates the binding creation time.
If NAT-Control-Binding-Status is set to Removed, Event-Timestamp
indicates the binding removal time. If NAT-Control-Binding-Status is
active, Event-Timestamp need not be present; if a value is present,
it indicates that binding is active at the given time.
NAT-Control-Record ::= < AVP Header: TBD >
{ NAT-Control-Definition }
{ NAT-Control-Binding-Status }
[ Event-Timestamp ]
9.2.2. NAT-Control-Binding-Status
The NAT-Control-Binding-Status AVP (AVP code TBD) is of type
enumerated. It indicates the status of the binding - created,
removed, or active.
The following values are defined:
Created (1)
NAT binding is created.
Active (2)
NAT binding is active.
Removed (3)
NAT binding was removed.
9.2.3. Current-NAT-Bindings
The Current-NAT-Bindings AVP (AVP code TBD) is of type Unsigned32.
It indicates the number of NAT bindings active on the NAT-device.
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Internet-Draft Diameter NAT Control Application September 201110. AVP Occurrence Table
The following sections present the AVPs defined in this document and
specify the Diameter messages in which they can be present. Note:
AVPs that can only be present within a Grouped AVP are not
represented in this table.
The table uses the following symbols:
0 The AVP MUST NOT be present in the message.
0+ Zero or more instances of the AVP can be present in the
message.
0-1 Zero or one instance of the AVP can be present in the
message. It is considered an error if there is more
than one instance of the AVP.
1 One instance of the AVP MUST be present in the message.
1+ At least one instance of the AVP MUST be present in the
message.
10.1. DNCA AVP Table for NAT Control Initial and Update Requests
The following table lists DNCA specific AVPs that have to be present
in NCRs and NCAs with NC-Request-Type set to INITIAL_REQUEST or
UPDATE_REQUEST.
+-------------------+
| Command Code |
+-----------------------------------+-------------------+
| Attribute Name NCR NCA |
+-------------------------------------------------------+
|NC-Request-Type 1 1 |
|NAT-Control-Install 0-1 0 |
|NAT-Control-Remove 0-1 0 |
|NAT-Control-Definition 0 0 |
|Current-NAT-Bindings 0 0 |
|Duplicate-Session-Id 0 0-1 |
+-------------------------------------------------------+
Note that any combination of "NAT-Control-Install" and "NAT-Control-
Remove" AVPs could be present in an update or initial requests.
Consider the following examples:
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Neither "NAT-Control-Install AVP" nor "NAT-Control-Remove AVP" are
present: This could for example be the case if the NAT-controller
would only want to receive accounting information, but not control
NAT-bindings.
Only "NAT-Control-Install AVP" is present: This could for example
be the case if a new NAT-binding is installed for an existing
session.
Only "NAT-Control-Remove AVP" is present: This could for example
be the case if a new NAT-binding is removed from an existing
session.
Both, "NAT-Control-Install AVP" and "NAT-Control-Remove AVP" are
present: This could for example be the case if a formerly created
NAT-binding is removed and a new NAT-binding is established within
the same request.
10.2. DNCA AVP Table for Session Query request
The following table lists DNCA specific AVPs that have to be present
in NCRs and NCAs with NC-Request-Type set to QUERY_REQUEST.
+-------------------+
| Command Code |
+-----------------------------------+-------------------+
| Attribute Name NCR NCA |
+-------------------------------------------------------+
|NC-Request-Type 1 1 |
|NAT-Control-Install 0 0 |
|NAT-Control-Remove 0 0 |
|NAT-Control-Definition 0 0+ |
|Current-NAT-Bindings 0 1 |
|Duplicate-Session-Id 0 0 |
+-------------------------------------------------------+
10.3. DNCA AVP Table for Accounting Message
The following table lists DNCA specific AVPs, which may or may not be
present in ACR and ACA messages.
+-------------------+
| Command Code |
+-----------------------------------+-------------------+
| Attribute Name ACR ACA |
+-------------------------------------------------------+
|NAT-Control-Record 0+ 0 |
|Current-NAT-Bindings 1 0 |
+-------------------------------------------------------+
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Internet-Draft Diameter NAT Control Application September 201111. IANA Considerations
This section contains the namespaces that have either been created in
this specification, or the values assigned to existing namespaces
managed by IANA.
In the subsections below, when we speak about review by a Designated
Expert, please note that the designated expert will be assigned by
the IESG. Initially, such Expert discussions take place on the AAA
WG mailing list.
11.1. Application Identifier
This specification assigns the value <TBD>, 'Diameter NAT Control
Application', to the Application Identifier namespace defined in
[RFC3588]. See Section 4 for more information.
11.2. Command Codes
This specification uses the value <TBD> from the Command code
namespace defined in [RFC3588] for the NAT-Control-Request (NCR),
NAT-Control-Answer (NCA) commands. See Section 6.1 and Section 6.2
for more information on these commands.
11.3. AVP Codes
This specification assigns the values <TBD> from the AVP code
namespace defined in [RFC3588]. See Section 8.7 for the assignment
of the namespace in this specification.
11.4. Result-Code AVP Values
This specification assigns the values <TBD> (4xxx, 5xxx, 5xxx, 5xxx,
5xxx,5xxx) from the Result-Code AVP value namespace defined in
[RFC3588]. See Section 8.2 for the assignment of the namespace in
this specification.
11.5. NC-Request-Type AVP
As defined in Section 8.7.1, the NC-Request-Type AVP includes
Enumerated type values 1 - 3. IANA has created and is maintaining a
namespace for this AVP. All remaining values are available for
assignment by a Designated Expert [RFC5226].
11.6. NAT-External-Port-Style AVP
As defined in Section 8.7.10, the NAT-External-Port-Style AVP
includes Enumerated type value 1. IANA has created and is
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maintaining a namespace for this AVP. All remaining values are
available for assignment by a Designated Expert [RFC5226].
11.7. NAT-Control-Binding-Status AVP
As defined in Section 8.7.1, the NAT-Control-Binding-Status AVP
includes Enumerated type values 1 - 3. IANA has created and is
maintaining a namespace for this AVP. All remaining values are
available for assignment by a Designated Expert [RFC5226].
12. Security Considerations
This document describes procedures for controlling NAT related
attributes and parameters by an entity, which is non-local to the
device performing NAT. This section discusses security
considerations for DNCA. This includes the interactions between the
Diameter peers within a NAT-controller and a NAT-device as well as
general considerations for NAT-control in a service provider network.
Security between a NAT-controller and a NAT-device has a number of
components: authentication, authorization, integrity, and
confidentiality.
Authentication refers to confirming the identity of an originator for
all datagrams received from the originator. Lack of authentication
of Diameter messages between the Diameter peers can jeopardize the
fundamental service of the peering network elements. A consequence
of not authenticating the message sender by the recipient would be
that an attacker could spoof the identity of a "legitimate"
authorizing entity in order to change the behavior of the receiver.
An attacker could for example launch a denial of service attack by
setting the maximum number of bindings for a session on the NAT-
device to zero; provision bindings on a NAT-device which include IP-
addresses already in use in other parts of the network; or request
session termination of the Diameter session and hamper a user's
connectivity. Lack of authentication of a NAT-device to a NAT-
controller could lead to situations where the NAT-device could
provide a wrong view of the resources (i.e. NAT-bindings). In
addition, NAT Binding Predefined template on the NAT-device could be
configured differently than expected by the NAT-controller. Failing
of any of the two DNCA Diameter peers to provide the required
credentials should be subject to logging. The corresponding logging
infrastructure of the operator SHOULD be built in a way that it can
mitigate potential denial of service attacks resulting from large
amounts of logging events. This could include proper dimensioning of
the logging infrastructure combined with policing the maximum amount
of logging events accepted by the logging system to a threshold which
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the system is known to be able to handle.
Authorization refers to whether a particular authorizing entity is
authorized to signal a network element requests for one or more
applications, adhering to a certain policy profile. Failing the
authorization process might indicate a resource theft attempt or
failure due to administrative and/or credential deficiencies. In
either case, the network element should take the proper measures to
log such attempts.
Integrity is required to ensure that a Diameter message exchanged
between the Diameter peers has not been maliciously altered by
intermediate devices. The result of a lack of data integrity
enforcement in an untrusted environment could be that an impostor
will alter the messages exchanged between the peers. This could
cause a change of behavior of the peers, including the potential of a
denial of service.
Confidentiality protection of Diameter messages ensures that the
signaling data is accessible only to the authorized entities. When
signaling messages between the DNCA Diameter peers traverse untrusted
networks, lack of confidentiality will allow eavesdropping and
traffic analysis.
Diameter offers security mechanisms to deal with the functionality
demanded above. DNCA makes use of the capabilities offered by
Diameter and the underlying transport protocols to deliver these
requirements (see Section 5.1). If the DNCA communication traverses
untrusted networks, messages between DNCA Diameter peers SHOULD be
secured using either IPsec or TLS. Please refer to [RFC3588],
section 13 for details. DNCA Diameter peers SHOULD perform bilateral
authentication, authorization as well as procedures to ensure
integrity and confidentiality of the information exchange. In
addition the Session-Id chosen for a particular Diameter session
SHOULD be chosen in a way that it is hard to guess in order to
mitigate issues through potential message replay.
DNCA Diameter peers SHOULD have a mutual trust setup. This document
does not specify a mechanisms for authorization between the DNCA
Diameter peers. The DNCA Diameter peers SHOULD be provided with
sufficient information to make an authorization decision. The
information can come from various sources, for example the peering
devices could store local authentication policy, listing the
identities of authorized peers.
Any mechanism or protocol providing control of a NAT-device, and DNCA
is an example of such a control mechanism, could allow for misuse of
the NAT-device given that it enables the definition of per-
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destination or per-source rules. Misuse could include anti-
competitive practices among providers, censorship, crime, etc. NAT-
control could be used as a tool for preventing or redirecting access
to particular sites. For instance, by controlling the NAT bindings,
one could ensure that end points aren't able to receive particular
flows, or that those flows are redirected to a relay that snoops or
tampers with traffic instead of directly forwarding the traffic to
the intended end point. In addition one could set up a binding in a
way that the source IP address used is one of a relay so that traffic
coming back can be snooped on or interfered with. The protections on
DNCA and its Diameter protocol exchanges don't prevent such abuses of
NAT-control. A service provider deploying DNCA needs to make sure
that higher layer processes and procedures are put in place which
allow them to detect and mitigate misuses.
13. Examples
This section shows example DNCA message content and exchange.
13.1. DNCA Session Establishment Example
Figure 15 depicts a typical call flow for DNCA session establishment.
In this example, the NAT-controller:
a. requests a maximum of 100 NAT-bindings for the end point.
b. defines a static binding for a TCP connection which associates
the internal IP-Address:Port 192.0.2.1:80 with the external IP-
Address:Port 198.51.100.1:80 for the end point.
c. requests the use of a preconfigured template called "local-
policy" while creating NAT-bindings for the end point.
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2. Based on the configuration of the DNCA Diameter peer within the
NAT-controller, the NAT-controller determines that NAT-control is
required and is to be enforced at a NAT-device.
3. If there is no Diameter session already established with the DNCA
Diameter peer within NAT-device, a Diameter connection is
established and Diameter Base CER/CEA are exchanged.
4. The NAT-Controller creates an NCR message (see below) and sends
it to the NAT-device. This example shows IPv4 to IPv4 address
and port translation. For IPv6 to IPv4 translation, the Framed-
IP-Address AVP would be replaced by the Framed-IPv6-Address AVP
with the value set to the IPv6 address of the end point.
< NC-Request > ::= < Diameter Header: TBD, REQ, PXY>
Session-Id = "natC.example.com:33041;23432;"
Auth-Application-Id = <DNCA Application ID>
Origin-Host = "natC.example.com"
Origin-Realm = "example.com"
Destination-Realm = "example.com"
Destination-Host = "nat-device.example.com"
NC-Request-Type = INITIAL_REQUEST
User-Name = "subscriber_example1"
Framed-IP-Address = "192.0.2.1"
NAT-Control-Install = {
NAT-Control-Definition = {
Protocol = TCP
Direction = OUT
NAT-Internal-Address = {
Framed-IP-Address = "192.0.2.1"
Port = 80
}
NAT-External-Address = {
Framed-IP-Address = "198.51.100.1"
Port = 80
}
}
Max-NAT-Bindings = 100
NAT-Control-Binding-Template = "local-policy"
}
5. The NAT-device establishes a DNCA session as it is able to comply
with the request.
6. The NAT-device sends an NCA to indicate the successful completion
of the request.
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<NC-Answer> ::= < Diameter Header: TBD, PXY >
Session-Id = "natC.example.com:33041;23432;"
Origin-Host = "nat-device.example.com"
Origin-Realm = "example.com"
NC-Request-Type = INITIAL_REQUEST
Result-Code = DIAMETER_SUCCESS
7. The end point sends packets that reach the NAT-device.
8. The NAT-device performs NAT for traffic received from the end
point with source address 192.0.2.1. Traffic with source IP-
address 192.0.2.1 and port 80 are translated to the external IP-
address 198.51.100.1 and port 80. Traffic with source IP-address
192.0.2.1 and a source port different from 80 will be translated
to IP-address 198.51.100.1 and a port chosen by the NAT-device.
Note that this example assumes that the NAT-device follows
typical binding allocation rules for end points, in that only a
single external IP-address is used for all traffic received from
a single IP-address of an end point. The NAT-device will allow a
maximum of 100 NAT-bindings be created for the end point.
13.2. DNCA Session Update with Port Style Example
This section gives an example for a DNCA session update: A new set of
NAT-bindings is requested for an existing session. The request
contains a directive ( the "NAT-External-Port-Style" AVP set to
FOLLOW_INTERNAL_PORT_STYLE) that directs the NAT-device to maintain
port-sequence and port-oddity for the newly created NAT-bindings. In
the example shown, the internal ports are UDP port 1036 and 1037.
The NAT-device follows the directive selects the external ports
accordingly. The NAT-device would for example create a mapping of
192.0.2.1:1036 to 198.51.100.1:5056 and 192.0.2.1:1037 to
198.51.100.1:5057, thereby maintaining port oddity (1036->5056,
1037->5057) and sequence ( the consecutive internal ports 1036 and
1037 map to the consecutive external ports 5056 and 5057).
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